With the progress of microfabrication of semiconductor devices, an EUV exposure technology using extreme ultraviolet (EUV) light, which has a short wavelength, has been developed. An EUV mask used for the EUV exposure is a light reflective mask, and has a pattern formed of a reflective portion, which reflects light, and an absorption portion, which absorbs light.
If there is a defect arising from irregularities of about several nanometers on a surface of the reflective portion of the EUV mask, the phase of the extreme ultraviolet light at the position is displaced, which may change dimensions or shape of a pattern transferred onto a semiconductor wafer.
Such minute irregularities are difficult to detect by observation using a normal scanning electron microscope (SEM) because the irregularities are buried in noise. For this reason, an atomic force microscope (AFM) is used for inspection of the EUV mask.
Japanese Laid-open Patent Publication No. 2012-112927 shows an example of such defect inspection apparatus and method.